This week, Professors Aideen Sullivan and Gerard O’Keeffe from University College Cork published an article in the Journal of the International Movement Disorders Society reporting on some pre-clinical (laboratory) data they have collected supporting the development of ‘Glial cell line-Derived Neurotrophic Factor’ (GDNF) as a potential disease-modifying treatment for Parkinson’s.

GDNF belongs to a family of naturally occurring proteins called neurotrophic factors (or nerve growth factors) that are critical in the development, growth and survival of nerve cells (or neurons) in the brain. Researchers believe that administration of neurotrophic factors into the brain may be able to promote the survival and rejuvenation of the dopamine-producing neurons that are lost as Parkinson’s progresses. Multiple lab-based studies and early-stage clinical trials involving GDNF have supported this hypothesis; however, we have yet to see these results replicated in a larger, placebo-controlled clinical trial in people with Parkinson’s.

Some researchers have suggested that this lack of replication of results in a larger trial may be due to a severe reduction in the number of ‘RET receptors’ observed in the brains of people with Parkinson’s. RET receptors are essential for GDNF to be able to have its protective effect on dopamine neurons. The absence of RET receptors may leave dopamine neurons more vulnerable, and GDNF administration ineffective.

This new data from Professors Sullivan and O’Keeffe reports that RET receptors are still produced and present in people with Parkinson’s, even in later stages of the disease. They propose that the previously reported reduction in RET receptors is a consequence of the loss of dopamine neurons overall, and it is the neurons themselves that produce RET receptors. This data also suggests that GDNF may still be able to have an effect in the brains of people with Parkinson’s and remains a viable experimental treatment approach for clinical trial; it is part of an ongoing pre-clinical lab-based study supported by Cure Parkinson’s evaluating whether Growth/Differentiation Factor 5 (or GDF5) – a nerve growth factor similar to GDNF – may have a disease-modifying effect in laboratory models of Parkinson’s. Unlike GDNF, GDF5 does not require RET receptors to have an effect, meaning the treatment would not rely on the amount of RET receptors remaining in the brains of people with Parkinson’s.

We look forward to seeing more developments as this project progresses.

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